Decorative laminates have been conventionally made by stacking a plurality of layers of paper impregnated with synthetic thermosetting resins. Normally, the assembly consists of a plurality (for example, three to eight) core sheets made from phenolic resin impregnated Kraft paper, above which lies a decor sheet, usually a print or solid color, impregnated with melamine resin. An overlay sheet is often provided on top of the decor sheet which, in the laminate, is made to be as transparent as possible and which provides protection for the decor sheet.
Early attempts to eliminate or simplify or improve the overlay sheet are exemplified in the Fuerst U.S. Pat. No. 3,373,071 and the Michl U.S. Pat. No. 3,135,643. The technique of these patents was to impregnate the decor sheet with plain melamine resin and then apply a thick coating to the surface of the impregnated sheet using a relatively viscous mixture of 2,000-60,000 cp. As a result, the viscous coating dried on the surface of the saturated decor sheet thus in essence forming an overlay sheet in situ. Insofar as is known, laminate made in this fashion never achieved substantial commercial utilization, except possibly for flooring material, possibly because the expense involved, including double handling, i.e. first saturating the impregnated sheet and then coating it, did not justify any modicum of improvement over the use of conventional overlay, or more probably because the resultant laminate was not of sufficient quality for commercial purposes, e.g. cracks, creasing, undue stiffness, insufficient overlay transparency, etc.
A later attempt to provide a more transparent yet fully protective layer over the decor sheet is discussed in the Chevallier U.S. Pat. No. 3,968,291 where barium sulfate is utilized as a particulate filler material in the cast in situ overlay sheet, the patentee having determined that barium sulfate has an index of refraction which is closer to the melamine resin than other fillers, thereby increasing the transparency of the overlayer and consequently the clarity of the decor sheet therebelow. This product also has never achieved any commercial acceptance, possibly for the same reasons as indicated above relative to the Fuerst and Michl patents.
More recently, the present art has been revolutionized by the development of the NEVAMAR ARP.RTM. technology, reference being made to Scher et al U.S. Pat. Nos. 4,255,480; 4,395,452; 4,430,375; Re 32,152; 4,263,081; 4,327,141; 4,400,423; Ungar et al U.S. Pat. Nos. 4,713,138; 4,517,235; 4,520,062; 5,037,694; 5,093,185; Lex et al U.S. Pat. No. 4,971,855; and O'Dell et al U.S. Pat. No. 4,499,137; 4,532,170; and 4,567,087. In the ARP.RTM. technology the overlayer which protects the decor sheet from abrasion is greatly reduced in thickness so as to provide a highly concentrated layer of abrasion resistant particles bound to the upper surface of the upper paper layer, usually the decor sheet. This technology not only provides improved abrasion resistance over earlier technologies, but provides increased transparency because of the ultra-thinness of the protective layer.
The ARP.RTM. technology has served the industry and the public very well, laminate product made according to this technology being recognized as a superior product and being in great demand. Among the Patents mentioned immediately above, the Lex et al U.S. Pat. No. '855 discloses a wear-resistant glossy laminate using the ARP.RTM. technology, but using abrasion-resistant mineral particles or grit having a particle size which is quite small so that substantially reduced, i.e. only little, scratching of the polished caul plates occurs during the pressing operation. While the glossy laminates of Lex et al U.S. Pat. No. '855 have excellent abrasion resistance considering the small particle size of the grit used, it would be desirable to be able to produce a glossy laminate, made using highly polished or mirror caul plates, having improved abrasion resistant properties and without causing any scratching and ultimate destruction of such highly polished caul plates. Up to the present invention, this has not been possible.